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Author Topic: Small Vibration Sensor? Help :)  (Read 2519 times)

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Offline GertlexTopic starter

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Small Vibration Sensor? Help :)
« on: December 11, 2008, 10:06:26 AM »
Hi folks.

I'm looking to build a circuit that is triggered by steady vibrations... specifically my cellphone on vibrate mode.

So I need some kind of vibration sensor, and small.  The circuit would then run a motor to produce larger vibrations.  Ideally, this circuit would drain minimal or no power when not running the motor.

I'm almost completely lacking in ideas.

The end goal is to have my cellphone's vibrations be amplified, to function much more effectively as an under-the-pillow alarm.  (And yes, there are pillow alarms. I had one, it stopped working after 6 months, and I'd prefer to build my own)

Help :D

Thanks,
•Gert
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Offline Trumpkin

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Re: Small Vibration Sensor? Help :)
« Reply #1 on: December 11, 2008, 10:14:41 AM »
Robots are awesome!

Offline GertlexTopic starter

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Re: Small Vibration Sensor? Help :)
« Reply #2 on: December 11, 2008, 10:23:57 AM »
Ohh thanks.

A piezoelectric sensor would be excellent, quite possibly.  I'm sure I could find just the piezo part, free of the phidgets board.  (Quick skim indicates that the Phidgets need to be run to a computer or processor.  I'm looking for a "dumb circuit" implementation, or maybe just an IC or two.

I'll throw an idea out now:
With the resulting voltage (big question is how much), I could trigger a MOSFET and start a circuit running.  What would be an approach for making the circuit keep itself running until turned off?  ... i.e. once the MOSFET is first triggered, bypass the MOSFET completely until switched off.  There's probably an IC that can do that, aye?

Mind's rolling here:
An IC with two inputs, one being connected to the battery, and the other connected to the MOSFET.  IC turns on when both give voltage high, and only resets itself when the first voltage goes low?
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Offline Soeren

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Re: Small Vibration Sensor? Help :)
« Reply #3 on: December 14, 2008, 02:46:43 PM »
Hi,


Here is a couple of circuits...

This one uses a relay. I'm not quite sure it will get to trigger the relay by the short piezo pulses, but this could be stretched.
The larger the piezo disk the better. It consume nothing but a tiny leakage current while off (a few nA at most).
http://That.Homepage.dk/PDF/PX_Detector_Relay.pdf


This one consumes a few µA when idle, but will probably be quicker to get up and running.
Pin 1 shouldn't need a pull-up, since the leakage through D1 and D3 should be enough.
This one is based on a design I made 7 or 8 years ago for a golf target "hit lamp" where the piezo disk was mounted on the backside of a thick steel plate.
http://That.Homepage.dk/PDF/PX_Detector.pdf


Assuming you have a pronounced hearing loss, did you consider a flashing lamp (or even a small xenon flash) as an add on?
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
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Offline GertlexTopic starter

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Re: Small Vibration Sensor? Help :)
« Reply #4 on: December 14, 2008, 03:01:24 PM »
Thank! I'll use those for reference.

I actually just bought some Piezo sensors last night, along with ICs containing 4 NAND or 4 NOR gates.

I'm currently planning to try using an SR Flip Flop to store the single bit of "on/off" data that is needed.

What is the part of the circuit with 4 NAND's called?  (I see that both NAND and NOR are used for different types of flash memory, basically)
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Offline Soeren

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Re: Small Vibration Sensor? Help :)
« Reply #5 on: December 14, 2008, 03:22:50 PM »
Hi,

I'm currently planning to try using an SR Flip Flop to store the single bit of "on/off" data that is needed.

What is the part of the circuit with 4 NAND's called?  (I see that both NAND and NOR are used for different types of flash memory, basically)
IC1A and IC1B, the 2 leftmost gates are indeed coupled as an SR-FF and the other two gates are just used as buffers even if not needed (the output could be taken from the other output of the FF with the same polarity as after the buffer gates), but otherwise their inputs just needed to be tied to a rail, so just as well use them.

A 4011 could be used instead of the 4093, I have just not used them for many years, since the 4093 can be used whenever the 4011B is called for and they have more uses due to the Schmitt trigger input.

Single gates are made (I have a few in SOT-23-like casings), but they are unfortunately not available to the hobbyist. Both 4011 and 4093 comes in SO14 as well as DIP14 however.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Admin

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Re: Small Vibration Sensor? Help :)
« Reply #6 on: January 09, 2009, 07:31:47 AM »
Hmmmm just buy a $13 accelerometer IC breakout board. Accelerometers can measure your vibration, you just need it to tell it what frequency to look for.

Offline pomprocker

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Re: Small Vibration Sensor? Help :)
« Reply #7 on: January 09, 2009, 11:15:48 AM »
I was going to say the same thing. The MEMS 2-axis accelerometer is sometimes used to detect vibration (or lack of vibration)

Offline GertlexTopic starter

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Re: Small Vibration Sensor? Help :)
« Reply #8 on: January 09, 2009, 11:18:04 AM »
I played around with this stuff over my break between semesters.  Never quite got a working circuit using the piezo switch to trigger the SR FF.... And I kinda lack the time to play with such or document any of my problems now :/
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